Danner supreme diaphragm replacement kit is designed to fit aquarium air pump 59943 ap-20. Diaphragm edge wall must be inserted in to the diaphragm retainer with the proper side facing into the groove in the retainer. The deeper side of the diaphragm will always face into the retainer groove. This kit includes diaphragms, flapper valves, plastic slip washers and bottom pressure chamber gasket; some models also include rubber plug sets to seal the flapper valve housing.